Decode-and-forward Mode Research Articles

Covert Communications in a Hybrid DF/AF Relay System.

In this paper, we study covert communications in a hybrid decode-and-forward (DF)/ amplify-and-forward (AF) relay system. The considered relay in normal operation forwards messages from a source node to a destination node in either DF or AF mode on request. Meanwhile, the source and destination nodes also attempt to secretly exchange covert messages such as confidential or sensitive information and avoid detection by the covert message detector embedded on the relay. We first establish an optimal DF/AF mode selection criterion to maximize the covert rate based on the analyses of delay-aware achievable covert rates of individual DF and AF modes. To further reduce the time complexity, we propose a low-complexity selection criterion as well for practical use. The numerical results demonstrate the covert rate gain as high as 50% and running time gain as high as 20% for particular system parameters, which verify the effectiveness of the proposed criteria.

On the Cooperative Relaying Strategies for Multi-Core Wireless Network-on-Chip

Recently, hybrid wired-wireless Network-on-Chip (WiNoC) has been proposed as a suitable communication fabric to provide scalability and satisfy high performance demands of the exascale era of modern multi/many-core System-on-Chip (SoC) design. A well accepted low-latency wireless communication fabric for WiNoCs is millimeter wave (mm-Wave). However, the wireless channel of mm-Wave is lossy due to free space signal radiation with both dielectric propagation loss (DPL) and molecular absorption attenuation (MAA). This is exacerbated for edge situated cores and in macro-chips embodying thousands of cores. To this end, this article proposes efficient relaying techniques to improve the signal strength of the wireless channel in the WiNoCs using on-chip networking approaches under the realistic SoC channel conditions. First, we propose a realistic relay communication channel for the WiNoCs to characterise both MAA and DPL which have drastic effect on the performance. We then derive and show that the channel capacity for a single-relay WiNoC employing Amplify-and-Forward (AF) and Decode-and-Forward (DF) relaying protocols increases by up to 20% and 25%, respectively, compared to the conventional direct transmission. The AF protocol outperforms the DF mode for shorter transmissions between the relay and the destination cores, while the reverse is observed in other conditions. A hybrid protocol is then proposed to exploit the performance advantages of both relaying protocols to address the unbalanced distance between the cores, providing the maximal channel capacity close to the cutset bound. Finally, our approach is further validated in multi-relay WiNoCs where the communications of the remote cores is assisted by multiple intermediate cores along with the details of associated realistic channel model in emerging many-core SoCs.

NOMA in Cooperative Communication Systems With Energy-Harvesting Nodes and Wireless Secure Transmission

In this paper, non-orthogonal multiple access (NOMA) in cooperative relay system is considered, where a source node communicates with a pair of energy harvesting (EH) user equipments through a multiple antennas relay node. A hybrid protocol is adopted at the relay, in which if the relay can successfully decode the signals, decode-and-forward (DF) protocol will be adopted to forward the signals to the users. Otherwise, amplify-and-forward (AF) protocol will be implemented. Assuming that the users adopt maximal ratio combining (MRC) to combine the received signals in the two cooperative phases, new explicit analytical expressions for the average sum-rate are derived when the relay works in, 1) AF mode, and 2) DF mode, in two scenarios when one user is the stronger in both cooperation phases, and when an alternative user is stronger in each phase. Then, the investigation is extended to the case where the relay is an untrusted node, and cooperative jamming technique is proposed to degrade the ability of the relay to decode the signals and enforce the relay to operate always in AF mode. For the untrusted relay scenario, new analytical expression for the average secrecy rate is derived. Monte Carlo simulations are provided to validate the analysis. The simulation results reveal that the location of the relay is the key parameter to achieve the best performance.

Exact analysis of the multihop multibranch hybrid AF/DF relaying networks

SummaryIn this paper, the exact analysis of a multihop multibranch (MHMB) relaying network is investigated wherein each relay can operate in amplify‐and‐forward (AF) or decode‐and‐forward (DF) modes depending upon the decoding result of its received signal. If a relay decodes the received signal correctly, it works in DF mode; otherwise, the relay operates in AF mode. Therefore, we name such relaying network as hybrid amplify‐and‐forward and decode‐and‐forward (hybrid AF/DF) relaying network. We first investigate the signal transmission from source to destination node via n number of relays in a hybrid AF/DF MHMB mode. Then, we obtained the statistical features and analyze the end‐to‐end signal‐to‐noise ratio (SNR). Finally, a comprehensive performance analysis is conducted by using maximal ratio combining (MRC) scheme at the destination node. For comparison, we also obtained the results using selection combining (SC) scheme at the destination node. To the best of our knowledge, very few works in the literature have considered a general system model of MHMB relaying network wherein each relay can operate in AF or DF modes, that is, a hybrid AF/DF relaying network. Accordingly, the analysis of our system model is not only novel and exact, but also is comprehensive and can be employed in the future works.

Relay Selection-aware Non-orthogonal Multiple Access Networks: Direct and Relaying Mode

Objective: In this paper, Decode-and-Forward (DF) mode is deployed in the Relay Selection (RS) scheme to provide better performance in cooperative downlink Non-orthogonal Multiple Access (NOMA) networks. In particular, evaluation regarding the impact of the number of multiple relays on outage performance is presented. Methods: As main parameter affecting cooperative NOMA performance, we consider the scenario of the fixed power allocations and the varying number of relays. In addition, the expressions of outage probabilities are the main metric to examine separated NOMA users. By matching related results between simulation and analytical methods, the exactness of derived formula can be verified. Results: The intuitive main results show that in such cooperative NOMA networks, the higher the number of relays equipped, the better the system performance can be achieved. Conclusion: DF mode is confirmed as a reasonable selection scheme to improve the transmission quality in NOMA. In future work, we will introduce new relay selections to achieve improved performance.

Exploiting hybrid decode-and-forward – amplify-and-forward in NOMA: an application to device-to-device networks

A novel model regarding downlink cooperative non-orthogonal multiple access (NOMA) in device-to-device network will be investigated in this paper, especially combining amplify-and-forward (AF) and decode-and-forward (DF) to achieve a hybrid scheme. We consider a remarkable trade-off between outage performances and power allocation factors. Especially, we study a hybrid AF and DF scheme, namely HDAF scheme for NOMA as follows: 1) The proposed scheme applies the AF scheme when the signal-to-interference-plus-noise ratio (SINR) at the relay is below a predefined threshold such that the relay cannot successfully decode the signal; 2) On the other hand, when the SINR at the relay is greater than the predefined threshold, the system will be applied the DF scheme to decode the signal and then forwards it to the destination, i.e., avoids noise and interference amplification at the relay. An analytical expression of the outage probability of the hybrid HDAF NOMA is derived based on the outage probability function in AF and DF mode. Numerical results are provided to illustrate the influence of network parameters such as transmit power, power constraint, and link distances on the outage probability.

Exploiting Hybrid Decode-and-Forward - Amplify-and-Forward in NOMA: An application to Device-To-Device Networks

A novel model regarding downlink cooperative non-orthogonal multiple access (NOMA) in device-to-device network will be investigated in this paper, especially combining amplify-and-forward (AF) and decode-and-forward (DF) to achieve a hybrid scheme. We consider a remarkable trade-off between outage performances and power allocation factors. Especially, we study a hybrid AF and DF scheme, namely HDAF scheme for NOMA as follows: 1) The proposed scheme applies the AF scheme when the signal-to-interference-plus-noise ratio (SINR) at the relay is below a predefined threshold such that the relay cannot successfully decode the signal; 2) On the other hand, when the SINR at the relay is greater than the predefined threshold, the system will be applied the DF scheme to decode the signal and then forwards it to the destination, i.e., avoids noise and interference amplification at the relay. An analytical expression of the outage probability of the hybrid HDAF NOMA is derived based on the outage probability function in AF and DF mode. Numerical results are provided to illustrate the influence of network parameters such as transmit power, power constraint, and link distances on the outage probability.

Throughput Maximization in Full-Duplex Dual-Hop Wireless Powered Communication Networks

In this paper, we consider a dual-hop wireless powered communication network (DH-WPCN) with a full duplex (FD) hybrid access point (HAP), which can transmit energy to the energy-constrained relays and receive information from the users assisted by the relays simultaneously. Under the setting, we propose an efficient relaying scheme, following which a relay can always harvest energy from the HAP only except the time slot that it forwards the user’s information to the HAP. After that, we investigate the system throughout maximization problems for both cases that the relays adopt the amplify-and-forward (AF) mode and the decode-and-forward (DF) mode. To obtain the optimal time allocation between the downlink energy transfer from HAP to relays and the uplink information transmission from users to HAP, we then propose a low-complexity algorithm to solve the formulated problems. Moreover, we prove that the DF mode leads to a higher system throughput than the AF mode theoretically. Simulation results demonstrate the superiority of the proposed scheme compared with the benchmark schemes.

New Beamforming and Relay Selection for Two-Way Decode-and-Forward Relay Networks

Multiple access broadcasting (MABC) is a spectral efficient protocol in a two-way relay channel (TWRC). The drawback of this protocol in decode-and-forward (DF) mode is decoding complexity at the relay side. Erroneous decoding at the relay can lead to error propagation that degrades the performance of all relay networks operating in the DF mode. In this paper, a maximum likelihood (ML) detector at the multiple-antenna relay is used, and it is proved that this decoding rule can achieve full diversity order at the multiple access (MAC) phase of the MABC protocol. Then, a new beamforming algorithm named as channel alignment is proposed, and it is shown that it achieves full diversity order. A new relay selection algorithm is proposed, and a tight upper bound for the bit error rate (BER) of this scheme is derived. It is proved that it achieves full diversity order. The analytical results and BER performance of the proposed schemes are investigated and compared through simulations.

Performance analysis of mixed amplify-and-forward and decode-and-forward protocol in underlay cognitive networks

In this paper, we propose and evaluate outage performance of a mixed amplify-and-forward (AF) and decode-and-forward (DF) relaying protocol in underlay cognitive radio. Different from the conventional AF and DF protocols, in the proposed protocol, a secondary source attempts to transmit its signal to a secondary destination with help of two secondary relays. One secondary relay always operates in AF mode, while the remaining one always operates in DF mode. Moreover, we also propose a relay selection method, which relies on the decoding status at the DF relay. For performance evaluation and comparison, we derive the exact and approximate closed-form expressions of the outage probability for the proposed protocol over Rayleigh fading channel. Finally, we run Monte Carlo simulations to verify the derivations. Results presented that the proposed protocol obtains a diversity order of three and the outage performance of our scheme is between that of the conventional underlay DF protocol and that of the conventional underlay AF protocol.

Capacity of OFDM Two-Hop Relaying Systems for Medium-Voltage Power-Line Access Networks

Orthogonal frequency-division multiplexing (OFDM) transmission is considered for a medium-voltage (MV) power-line access network (AN). In this paper, we analyze the channel capacity of OFDM-based two-hop relaying systems over MV power lines, where a single relay node is used between the source and destination nodes in an effort to enhance the channel capacity using either cooperative relaying (CR) or noncooperative relaying protocols. For each relaying protocol, the relay node operates in either the amplify-and-forward (AF) or the decode-and-forward (DF) mode. Numerical results show that the channel capacity of the CR protocol in the DF mode is superior to that in the AF mode, as well as to the NCR protocol in the AF and DF modes.